Parton dynamics in heavy-ion collisions from FAIR to LHC Wolfgang Cassing Erice, 21.09.2012
The holy grail: Search for the critical point The phase diagram of QCD Study of the phase transition from hadronic to partonic matter Quark-Gluon-Plasma Study of the in-medium properties of hadrons at high baryon density and temperature Study of the partonic medium beyond the phase boundary 2
Signals of the phase transition: Multi-strange particle enhancement in A+A Charm suppression Collective flow (v 1, v 2, v 3, v 4 ) Thermal dileptons Jet quenching and angular correlations High p T suppression of hadrons Nonstatistical event by event fluctuations and correlations Chiral Magnetic Effect? Experiment: measures final hadrons and leptons How to learn about physics from data? Compare with theory! Microscopic transport models provide a unique dynamical description of nonequilibrium effects in heavy-ion collisions!
From hadrons to partons In order to study the phase transition from hadronic to partonic matter Quark-Gluon-Plasma we need a consistent non-equilibrium (transport) model with explicit parton-parton interactions (i.e. between quarks and gluons) beyond strings! explicit phase transition from hadronic to partonic degrees of freedom lqcd EoS for partonic phase Transport theory: off-shell Kadanoff-Baym equations for the Green-functions S < h(x,p) in phase-space representation for the partonic and hadronic phase Parton-Hadron-String-Dynamics (PHSD) QGP phase described by Dynamical QuasiParticle Model (DQPM) W. Cassing, E. Bratkovskaya, PRC 78 (2008) 034919; NPA831 (2009) 215; W. Cassing, EPJ ST 168 (2009) 3 A. Peshier, W. Cassing, PRL 94 (2005) 172301; Cassing, NPA 791 (2007) 365: NPA 793 (2007)
The Dynamical QuasiParticle Model (DQPM) Basic idea: Interacting quasiparticles - massive quarks and gluons (g, q, q bar ) with spectral functions : E 2 = p 2 +M 2 -γ 2 mass: width: quarks gluons: A. Peshier, PRD 70 (2004) 034016 N c = 3, N f =3 running coupling: α S (T) = g 2 (T)/(4π) fit to lattice (lqcd) results (e.g. entropy density) with 3 parameters: T s /T c =0.46; c=28.8; λ=2.42 α S (T) 2.5 2.0 1.5 1.0 0.5 0.0 N τ =8 lqcd: O. Kaczmarek et, PRD 72 (2005) 059903 1 2 3 4 5 6 7 8 9 10 quasiparticle properties (mass, width) T/T C DQPM: Peshier, Cassing, PRL 94 (2005) 172301; Cassing, NPA 791 (2007) 365: NPA 793 (2007) 5
DQPM thermodynamics (N f =3) and lqcd entropy pressure P interaction measure: energy density: lqcd: Wuppertal-Budapest group Y. Aoki et al., JHEP 0906 (2009) 088. T C =160 MeV ε C =0.5 GeV/fm 3 p/ε 0.35 0.30 0.25 0.20 0.15 N f =3 0.10 0.05 DQPM gives a good description of lqcd results! equation of state 0.00 1 10 100 1000 ε [GeV/fm 3 ] 6
The Dynamical QuasiParticle Model (DQPM) Quasiparticle properties: large width and mass for gluons and quarks Broad spectral function : DQPM matches well lattice QCD DQPM provides mean-fields (1PI) for gluons and quarks as well as effective 2-body interactions (2PI) DQPM gives transition rates for the formation of hadrons PHSD Peshier, Cassing, PRL 94 (2005) 172301; Cassing, NPA 791 (2007) 365: NPA 793 (2007)
PHSD - basic concept Initial A+A collisions HSD: string formation and decay to pre-hadrons Fragmentation of pre-hadrons into quarks: using the quark spectral functions from the Dynamical QuasiParticle Model (DQPM) - approximation to QCD Partonic phase: quarks and gluons (= dynamical quasiparticles ) with off-shell spectral functions (width, mass) defined by the DQPM elastic and inelastic parton-parton interactions: using the effective cross sections from the DQPM q + qbar (flavor neutral) <=> gluon (colored) gluon + gluon <=> gluon (possible due to large spectral width) q + qbar (color neutral) <=> hadron resonances self-generated mean-field potential for quarks and gluons! Hadronization: based on DQPM - massive, off-shell quarks and gluons with broad spectral functions hadronize to off-shell mesons and baryons: gluons q + qbar; q + qbar meson (or string); q + q +q baryon (or string) (strings act as doorway states for hadrons) Hadronic phase: hadron-string interactions off-shell HSD W. Cassing, E. Bratkovskaya, PRC 78 (2008) 034919; NPA831 (2009) 215; EPJ ST 168 (2009) 3; NPA856 (2011) 162. 8
PHSD: Hadronization details Local covariant off-shell transition rate for q+qbar fusion => meson formation using N j (x,p) is the phase-space density of parton j at space-time position x and 4-momentum p W m is the phase-space distribution of the formed pre-hadrons : (Gaussian in phase space) is the effective quark-antiquark interaction from the DQPM Cassing, Bratkovskaya, PRC 78 (2008) 034919; Cassing, EPJ ST 168 (2009) 3 9
Collective flow: anisotropy coefficients (v 1, v 2, v 3, v 4 ) in A+A almond shaped interaction zone?
Initial participants and spectators in event by event calculations In each event the reaction plane is tilted in coordinate space and of irregular shape higher order harmonics!
Final angular distributions of hadrons S. A. Voloshin show higher order harmonics v n
Excitation function of elliptic flow is not described by hadron-string or purely partonic models!
Elliptic flow from PHSD versus STAR/PHENIX is reasonably described by PHSD due to an increasing fraction of partonic degrees-of-freedom! V. P. Konchakovski et al., PRC 85 (2012) 044922
Flow coefficients versus centrality increase of v 2 with impact parameter but rather flat v 3 and v 4 V. P. Konchakovski et al., PRC 85 (2012) 044922
More excitation functions Very low v 3 and v 4 at FAIR energies Almost constant v 4 /(v 2 ) 2 for PHSD V. P. Konchakovski et al., PRC 85 (2012) 044922
In-plane flow v 1 versus beam energy versus centrality PHSD: v 1 vs. pseudo-rapidity follows an approximate scaling for high invariant energies s 1/2 =39, 62, 200 GeV - in line with experimental data whereas at low energies the scaling is violated! V. P. Konchakovski et al., PRC 85 (2012) 044922
Transverse momentum dependence elliptic flow triangular flow needs partonic degrees-of-freedom! V. P. Konchakovski et al., PRC 85 (2012) 044922
Ratio v 4 /(v 2 ) 2 vs. p T is very sensitive to the microscopic dynamics! V. P. Konchakovski et al., PRC 85 (2012) 044922
Elliptic flow scaling at RHIC The mass splitting at low p T is approximately reproduced as well as the meson-baryon splitting for p T > 2 GeV/c! The scaling of v 2 with the number of constituent quarks n q is roughly in line with the data. E. Bratkovskaya, W. Cassing, V. Konchakovski, O. Linnyk, NPA856 (2011) 162 20
Shear viscosity from PHSD in a box
Transport coefficients Cross sections in PHSD
Summary PHSD provides a consistent description of off-shell parton dynamics in line with the lattice QCD equation of state PHSD versus experimental observables: enhancement of meson m T slopes (at top SPS and RHIC) strange antibaryon enhancement (at SPS) partonic emission of high mass dileptons at SPS and RHIC enhancement of collective flow v 2 with increasing energy quark number scaling of v 2 (at RHIC) jet suppression near-side ridge evidence for strong partonic interactions in the early phase of relativistic heavy-ion reactions from FAIR to LHC energies initial fluctuations generate odd flow components! Shear viscosity to entropy density has a minimum close to Tc. Collective flow is also generated by the scalar partonic mean-field!
PHSD group Wolfgang Cassing (Giessen Univ.) Volodya Konchakovski (Giessen Univ.) Olena Linnyk (Giessen Univ.) Elena Bratkovskaya (FIAS & ITP Frankfurt Univ.) Vitalii Ozvenchuk (HGS-HIRe, FIAS & ITP Frankfurt Univ.) Rudy Marty (Frankfurt Univ.) External Collaborations: SUBATECH, Nantes Univ. : Jörg Aichelin Christoph Hartnack Pol-Bernard Gossiaux Texas A&M Univ.: Che-Ming Ko JINR, Dubna: Vadim Voronyuk Viatcheslav Toneev Kiev Univ.: Mark Gorenstein Barcelona Univ. Laura Tolos, Angel Ramos
Outlook - Perspectives What is the stage of matter close to T c at finite quark chemical potential: Lattice EQS crossover, T > T c 1st order phase transition? Mixed phase = interaction of partonic and hadronic degrees of freedom? Open problems: How to describe a first-order phase transition in transport models? How to describe parton-hadron interactions in a mixed phase? A possible solution (?) : mixed phase description within molecular dynamics?
Dileptons are produced throughout all reaction phases!
Dileptons at SPS: NA60 Fireball model Renk/Ruppert Fireball model Rapp/vanHees Hydro model Dusling/Zahed Parton-Hadron-String-Dynamics microscopic transport model - PHSD good agreement with data in shape and absolute yield Mass region above 1 GeV is dominated by partonic radiation Contributions of 4π channels (radiation from multi-meson reactions) are small O. Linnyk, E. Bratkovskaya, V. Ozvenchuk, W. Cassing and C.M. Ko, PRC 84 (2011) 054917 NA60 Collaboration, Eur. Phys. J. C 59 (2009) 607; CERN Courier 11/2009
The rise and fall of radial flow of thermal dimuons NA60: Phys. Rev. Lett. 100 (2008) 022302 S. Damjanovic, Trento 2010: Strong rise of T eff with dimuon mass, followed by a sudden drop for M>1 GeV: Rise consistent with radial flow of a hadronic source (here π + π ρ µ + µ ), taking the freeze-out as the reference ( from a separate analysis of the ρ peak and the continuum) The drop of T eff signals a sudden transition to a low-flow source, i.e. a source of partonic origin (here qqbar µ + µ ) NA60: Dileptons for M >1 GeV are of dominantly partonic origin! 28
PHENIX: mass spectra Peripheral collisions (and pp) are well described, however, central fail! O. Linnyk, W. Cassing, J. Manninen, E.B. and C.-M. Ko, PRC 85 (2012) 024910
PHENIX: p T spectra The lowest and highest mass bins are described very well Underestimation of p T data for 100<M<750 MeV bins consistent with dn/dm The missing source (?) is located at low p T! O. Linnyk, W. Cassing, J. Manninen, E.B. and C.-M. Ko, PRC 85 (2012) 024910
STAR: dilepton mass spectra STAR data are well described Confirmed by the extended data set at QM2012 O. Linnyk, W. Cassing, J. Manninen, E.Bratkovskaya and C.M. Ko, PRC 85 (2012) 024910
PHENIX: mass spectra with HBD Peripher al Semicentral Preliminary PHENIX data with Hadron-Blind Detector (HBD) presented at QM 2012 Room for the QGP yield at M>1 GeV and for the in-medium modification of rho at low mass I. Tserruya for PHENIX Collaboration, Quark Matter 2012
Predictions for LHC dn/dm [1/(GeV/c 2 )] 10 2 10 1 10 0 10-1 10-2 10-3 Pb+Pb, s 1/2 =2.76 TeV, b=0.5, y <0.88 PHSD ω φ J/Ψ 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 M [GeV/c 2 ] π 0 η ρ ω φ J/Ψ, Ψ' DD DD correlated BB QGP ( qq ) Sum Ψ' dn/dm [1/(GeV/c 2 )] 10 1 10 0 10-1 10-2 10-3 10-4 Pb+Pb, s 1/2 =2.76 TeV, b=0.5, y <0.88, p T e >1 GeV 10 2 PHSD ω φ 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 M [GeV/c 2 ] π 0 η ρ ω φ J/Ψ, Ψ' DD BB QGP ( qq ) Sum J/Ψ Ψ' QGP(qbar-q) dominates at M>1.2 GeV p T cut enhances the signal of QGP(qbar-q) D-, B-mesons energy loss from Pol-Bernard Gossiaux and Jörg Aichelin JPsi and Psi nuclear modification from Che-Ming Ko and Taesoo Song O. Linnyk et al. arxiv:1208.1279 (2012)